Online In Situ Real-Time Experimental Investigation of the Crystallization Characteristics and Kinetic Models during the Nucleation and Growth Process of Para-Xylene Suspension Crystallization

The environmentally friendly and efficient preparation of high-purity P-xylene (PX) through suspension crystallization technology holds great significance for further advancement of the petrochemical industry. This review innovatively conducts experimental research on the entire process of PX intermittent suspension crystallization without the addition of crystal seeds in order to further clarify the details of the PX crystallization behavior. Online in situ imaging technology is used for the first time to monitor the real-time changes in the shape and particle size information on PX crystals during the crystallization process of low melting point xylene systems. Then, we derive the nucleation and growth kinetic equations of PX crystallization without adding seeds and further explore its crystallization kinetics and thermodynamic mechanism. The results can be concluded as follows. The PX crystal shape is primarily regular elongated rectangles. Without the addition of seeds, the crystal number and size rapidly increase at the moment of nucleation, the final average particle size is around 425 mu m. The solution supersaturation decreased rapidly in the initial stage of crystallization and stabilized after 20 min. As the stirring speed increases, the crystal aggregation decreases, the fragmentation degree increases, and the average particle size decreases monotonically. The crystal purity is highest at 400 rpm. The mechanism by which stirring speed affects the particle size distribution of PX crystals will vary with changes in the crystallization time. The fitted crystallization kinetic equations can accurately reflect the actual nucleation and growth rates. This work is expected to theorize, model, and parametrize the PX suspension crystallization process.